In ACM Transactions on Graphics (Proceedings of SIGGRAPH), 2014

We present a new rendering algorithm, unified points, beams, and paths (UPBP), for light transport simulation in participating media. UPBP combines a number of volumetric estimators based on points and beams with Monte Carlo path sampling techniques, all of which have complementary strengths and weaknesses. (Scene inspired by Gkioulekas et al. [2013].)

Abstract

Efficiently computing light transport in participating media in a manner that is robust to variations in media density, scattering albedo, and anisotropy is a difficult and important problem in realistic image synthesis. While many specialized rendering techniques can efficiently resolve subsets of transport in specific media, no single approach can robustly handle all types of effects. To address this problem we unify volumetric density estimation, using point and beam estimators, and Monte Carlo solutions to the path integral formulation of the rendering and radiative transport equations. We extend multiple importance sampling to correctly handle combinations of these fundamentally different classes of estimators. This, in turn, allows us to develop a single rendering algorithm that correctly combines the benefits and mediates the limitations of these powerful volume rendering techniques.